ggml: Add basic SET_ROWS support in WebGPU

[reeselevine]

This allows the CI to run using SET_ROWS instead of CPY.

• Adds basic SET_ROWS f32-> f16 shader/setup
• Since WGSL does not support 64-bit values, an error should be reported if a SET_ROWS index is > 2^32.
• To do this, an error value is set in the shader, and GGML_ABORT is called when a later callback sees that there has been an error.
• This PR also adds code for setting up a debug buffer, which can be useful for understanding what's going on in shaders while developing.